Patients with anxiety spectrum disorders are a highly heterogeneous group, requiring new therapeutic strategies and individualized treatment monitoring. Today, there is a growing interest for implementing biological approaches to clinical practice in psychiatry. Quantitative EEG is an excellent tool in this regard, though it has been widely underestimated when compared to recent neuroimaging techniques. In this case series, we presented four cases with a different diagnosis of anxiety spectrum disorder and evaluated their qEEG changes before and after the treatment. In addition, we also calculated the so-called EEG cordance values as an index of cerebral perfusion and cingulate cortex activity. According to the results, there appears to be an increase in the frontal beta and theta band in our cases, which has responded to treatment. In regards to the cordance values, we found that there was a reduction in the prefrontal regions up to %38 percent following the treatment. Based on previous studies, this may also indirectly suggest reduction in the cingulate cortex activity. The possible implications of these findings were discussed. Taken together, this case series highlighted the potential use of qEEG power values, normative z-scores and cordance values in treatment response monitoring of anxiety spectrum disorders.